1. Field of the Invention
The present invention relates to a centrifuge which separates, by centrifugation, fine particles in a liquid sample in which separation-target particles are mixed.
2. Description of the Related Art
In the fields of biology, medical science, agriculture, and the like, a zonal centrifugation method is used in order to separate fine particles like intracellular materials or viruses. According to the zonal centrifugation method, one which is called a swing rotor (or swinging bucket rotor) and which rotates with a plastic test tube filled with a sample being inserted into a bucket of the rotor is used.
A product so-called a zonal rotor is also sold and used instead of the swing rotor. As such a product, a P35ZT-type zonal rotor made by Hitachi Koki, Co., Ltd. is commercially available. The zonal rotor has characteristics such that it has little turbulence of a sample since there is no “wall effect”, has a large capacity, and continuously allows filling of a sample, collection thereof and analytical operation when rotating in comparison with the swing rotor. The zonal rotor is mainly used for separation needing a great capacity and a high precision like vaccine production. An explanation will now be given of a configuration of a conventional centrifuge having the zonal rotor.
FIGS. 5A and 5B are diagrams showing a whole configuration of a conventional centrifugal separation device (hereinafter, “centrifuge”) 51a having a zonal rotor (hereinafter, “rotor”) 10. FIG. 5A shows a state when a sample is filled/collected, while FIG. 5B shows a state when centrifugal separation is carried out. As shown in FIG. 5A, the centrifuge 51a comprises a driving unit 53, the rotor 10 and a rotor rotation chamber 55 all arranged inside a casing 52 formed of sheet-metal parts, a control panel 57 indicating a driving state, and, an electrical control unit 60, a vacuum evacuation device 62, and a rotor-chamber-interior cooling device 64 which are illustrated with a simplified contour respectively in the figure.
The rotor 10 stores a separation-target sample 184 shown in FIG. 6, and as the rotor 10 is rotated and driven by the driving unit 53, the rotor 10 separates the sample 184 in such a way that the sample 184 forms layers in the radial direction. As shown in FIGS. 5A, 5B and FIG. 6, the rotor 10 mainly comprises a bowl-like rotor body 12, partition walls (hereinafter, “septa”) 16a arranged in the rotor body 12 and dividing a sample storage chamber 18 into sector forms as viewed from the above, and a cover 14a having a female thread fastened with a male thread provided on an upper external face of the rotor body 12, functioning as a lid, and provided with an opening at the center thereof where a shaft 70a passes all the way through.
As shown in FIG. 6, the shaft 70a is formed in a cylindrical shape, and a lower end thereof is fixed to an internal bottom face of the rotor body 12. An upper end of the shaft 70a is attached with a rotating seal (first sealing member) 72 used for taking out/putting in the sample 184. The shaft 70a has a sample passageway 300 and an extrusion liquid passageway 320. The sample passageway 300 runs from an opening formed in the upper end of the shaft 70a to an opening formed in a side face of the shaft 70a and located in the interior of the rotor 10. The extrusion liquid passageway 320 penetrates the septa 16a in the radial direction of the rotor 10 from the upper end of the shaft 70a, and is communicated with a space between the rotor 10 and the septa 16a. 
When centrifugal separation is carried out, the rotor 10 is mounted in such a way that a rotation shaft opening 120 shown in FIG. 6 is connected to a rotation shaft 54 provided upwardly of the driving unit 53 shown in FIG. 5A. Thereafter, in accordance with the steps and procedures shown in FIG. 7, the centrifuge 51a is operated. Then, a target is separated by centrifugation and collected. An explanation will be given of operation steps of the rotor 10 with reference to FIG. 7.
At a step of “filling a sample”, a seal member 76 is attached with the rotor 10 being rotating at about 3000 rpm in an atmosphere. The seal member 76 is caused to contact and slide the rotating seal 72 of the rotor 10 to configure a mechanical seal. Next, using a liquid-feeding pump (not shown), a separation-target sample 184 and a density gradient liquid necessary for separating the sample 184 are filled. The seal member 76 is attached to a seal supporting plate 58 attached in the rotor rotation chamber 55 in such a manner as to be coaxial with a rotation axis of the rotor 10. Thereafter, the sample 184 is filled into a central part of the rotor 10 through the sample passageway 300 shown in FIG. 6, and then a preparation for centrifugal separation is completed. This operation is carried out with a door 56a of the centrifuge 51a being opened.
Next, at a step of “centrifugal separation” shown in FIG. 7, the seal member 76 is removed, and a cap 74 is attached to a leading end of the shaft 70a shown in FIG. 6 in order to airtightly sealing the interior of the rotor 10. The cap 74 is attached to the upper end of the shaft 70a while being sealed with an O-ring or the like. When the rotor 10 is rotated at high speed to perform centrifugal separation on the sample 184, the door 56a is closed, the rotor rotation chamber 55 is vacuumed (depressurized) by the vacuum evacuation device 62 shown in FIG. 5A, so that generation of heats due to friction of the rotor 10 with the air is suppressed. However, when the centrifuge 51a is operated under a depressurized condition, the sample 184 in the rotor 10 is likely to be evaporated. The cap 74 is used in order to suppress such evaporation. Next, the rotor rotation chamber 55 is vacuumed, the rotation speed of the rotor 10 is increased to a predetermined rotation speed, and centrifugal separation with a time appropriate for separation of the sample 184 is carried out.
After the centrifugal separation, at a step of “collecting the sample” shown in FIG. 7, the rotation speed of the rotor 10 is reduced again to 3000 rpm, and the pressure of the rotor rotation chamber 55 is returned back to the atmospheric pressure. Thereafter, the door 56a is opened, the cap 74 is removed, the sealing member 76 is attached again, and the separated liquid in the rotor 10 is collected. For example, in the case of sample collection at 3000 rpm, a liquid having a large density (hereinafter, “extrusion liquid”) is fed from an external wall side in the rotor 10 through the extrusion liquid passageway 320 of the shaft 70a. The sample 184 is ejected to the exterior through the sample passageway 300 of the shaft 70a, and collected. A density gradient liquid containing settled-out particles can be dividingly collected by a fraction collector while continuously measuring a light absorption degree by a spectrophotometrical meter. At this time, the sealing member 76 and the rotating seal 72 at the rotor 10 side contact with each other, so that sealing is accomplished in order to suppress any leakage of the liquid.
As explained above, such a centrifuge is used for the purposes of virus purification to produce a vaccine and elimination of fever-inducing agents. Specific examples of the sample 184 are influenza viruses, Japanese B encephalitis viruses, whooping-cough viruses, AIDS viruses, and hepatitis viruses, and a staring ingredient thereof is a cell picked up form a culture fluid or an animal, or one suspended in a liquid like a biological fluid.
U.S. Pat. No. 4,011,972 discloses a continuous flow centrifugal separation rotor which performs centrifugal separation while allowing a sample to be continuously flowed into a rotor which is rotating at high speed. A rotor main body is arranged in a rotor rotation chamber, and a mechanical seal member is arranged outwardly of a door of a centrifuge. A journal bearing is provided around an outer circumference of a tube member extending upwardly from the rotor and having plural sample passageways. A space between the outer circumference of the tube and the bearing is lubricated by a lubricant. The lubricant functions to disconnect the interior of the rotor rotation chamber and the exterior thereof, and to maintain a vacuum environment in the rotor rotation chamber. One mechanical seal member has a sealing configuration that a rotating seal and a fixation seal always contact with each other. According to U.S. Pat. No. 4,011,972, a sample is continuously filled in at a predetermined flow rate and collected while the rotor is in a high-speed rotation condition, so that such a rotor is called a continuous flow rotor. An example of such a commercially available rotor is a P32CT-type continuous rotor made by Hitachi Koki Co., Ltd.
According to the zonal centrifuge, it requires an attachment/removal work of a cap and a seal member to a shaft which is rotating in conjunction with a rotor. Such a work to the rotating shaft cannot be carried out efficiently if an operator is not skilled well even if the rotor is rotated at a low rotation speed.
Moreover, according to the conventional centrifuge 51a, when a density gradient liquid and an extrusion liquid are filled and when the sample 184 is filled or collected, the rotor rotation chamber 55 is kept in an atmospheric pressure (with the door 56a being opened). Accordingly, airs flow into the rotor rotation chamber 55, so that the interior of the rotor rotation chamber 55 is subjected to dew condensation, or temperature control becomes imperfect.
Further, according to the continuous rotor disclosed in U.S. Pat. No. 4,011,972, since the seal member is always in a contact condition, the seal member is easily worn, and a lifetime thereof is short.